1. Field of the Invention
The present invention relates generally to the field of hydrogenation processes, and more particularly but not by way of limitation, to methods and apparatus for improved control and processing of a continuous hydrogenation reaction for unsaturated oils.
2. Discussion
The process of hydrogenation, as practiced on feedstocks of small grain, edible oils, has made a wide variety of products available which were formerly made exclusively from animal fats and oils. Hydrogenation has thusly taken on great economic importance as it has been utilized to make highly popular, healthful food substances available to the world's population. Its utility in the production of plastic products has long been known, hydrogenation has also become very beneficial in its provision of highly unsaturated oils having greater stability from oxidation.
There are two limiting factors that must be considered when dealing with hydrogenation, with these factors dependent upon the desired character of the finished product and the nature of the oil feedstock utilized in the hydrogenation process. The first factor to be considered is the degree and kind of isomerization desired for the finished product. It turns out that there is a direct correlation between the amount of trans-isomerization produced and the degree of plasticity of most oils at a given congealing temperature. While the term plasticity is used herein, it is recognized that this attribute is also sometimes referred to as the hardening characteristic of an oil. It is measured by the Solid Fat Index, a parameter measured by testing protocol established by the American Oil Chemists Society Method No. Cd 10-57.
The second of these process factors is the degree of hydrogenation. The propensity of the polyunsaturated oil to bond with hydrogen is measured with a titration called the Iodine Value of the oil. As hydrogenation proceeds, double bonds of unsaturated components of the feedstock oil are replaced with hydrogen to form ethylene groups, thus lowering the level of unsaturation. The function of hydrogenation, in addition to reducing the degree of unsaturation, should also be to selectively hydrogenate trienes and dienes without the process going to complete saturation. Hence, it is desirable that hydrogenation be carried on under conditions having favorable Selectivity Ratios. High Selectivity Ratios are preferable for the reason that a process can be stopped or limited more accurately with the greatest or desired level of monoenes achieved. The degree of unsaturation--the Iodine Value--is measured by the testing protocol of the American Oil Chemists Society Method No. Cd 1-15. This time consuming procedure provides a time delayed process measurement which is unsuitable for continuous hydrogenation control.
Equipment and procedures for the continuous hydrogenation of edible oils to provide true flexibility in the control of the amount of, and selectivity of, hydrogenation and the control of the degree of transisomerization, does not exist today. In order that a feedstock oil be hydrogenated so as to produce a tailored product having predetermined characteristics, one must be able to control the degree of isomerization while simultaneously obtaining a suitable Selectivity Ratio and degree of hydrogenation, and further, be able to identify and control these factors while the process is continuing. The equipment required for continuously hydrogenating small grain edible oils must have the ability to measure the product quality changes that are occurring within the process equipment, as well as to predict the final quality of the product produced. Such equipment must also have the ability to make measurements on the controlling parameters of the process to achieve optimal performance of the process equipment. That is, there is a need to obtain measurements representing the quality profile of the product as well as to obtain measurements that are utilized to control the process dynamics.
While no prior art hydrogenation process has achieved the above stated control of continuous hydrogenation, there are some that have made claim to continuous hydrogenation of unsaturated oils, such as Mills et al. U.S. Pat. No. 2,520,425 issued Aug. 29, 1950 and companion U.S. Pat. Nos. 2,520,422 and 2,520,423 issued on even date therewith. The continuous hydrogenator of Mills et al. features a vertically extending central shaft with horizontally extending agitator blades meshing with spatially disposed stator blades which are designed to shear the rising processing fluid as same is caused to pass around multiple stator blades. However, since the fluid is a slurry of oil and suspended catalyst, the centrifugal force imparted to the mixture stratifies the mixture so that there exists a near vacant conduit which permits the passage of unreacted hydrogen up and along the rotating shaft; this is especially evident when one considers the rotational speeds suggested by Mills et al. up to 1000 rotations per minute. Mills et al. uses only standard quality measurements, such as Iodine Values, and does not present any teaching of dynamic testing; accordingly, the continuous hydrogenation processes taught by these prior art patents are of limited use and have not gained widespread acceptance.
U.S. Pat. No. 3,792,067, issued to Coombes et al. on Feb. 12, 1974, taught a process for continuous hydrogenation of fatty oils wherein an oil and dispersed catalyst mixture is passed through a pipeline reactor. Hydrogen is introduced at spaced intervals along the length of the reactor. Coombes et al. maintains two-phase flow and relies on fluid turbulence alone for agitation.
U.S. Pat. No. 3,634,471, issued to Kehse on Jan. 11, 1972, taught a method for continuous hydrogenation of oils and fats in which the oil is caused to flow over horizontally extending perforated plates. Hydrogen, generated by an electrolyzer, is passed upwardly through the oil which is caused to flow in a determined depth horizontally over the trays as it overflows each tray to move from top to bottom in the hydrogenator. Cooling is effected by cooling pipes arranged to contact the outside wall of the hydrogenator. Hydrogen production is responsive to vessel pressure, and thus Kehse claims that such corresponds to the concurrent consumption of hydrogen gas in the hydrogenator vessel.